A friend of mine had PC fan failure recently. She described it as "a loud grinding sound." Usually, when fans fail, they sound more like jet engines about to take off. OK OK, they sound like they're about to explode and I suppose you could describe that as somewhat of a grinding sound. Usually, it's the excessive and extremely loud werring sound we describe as "like a plane taking off." Or somewhat like this:
Lol that sounds like the space shuttle taking off!